Detection of chemical species in gas or vapor phases is a rapidly growing field. Toxic chemicals, such as hydrogen cyanide and nitrogen dioxide, are released during combustion or pyrolysis. If not properly exhausted, these chemicals can accumulate, eventually reaching dangerous levels. Other chemicals, such as acetone and various exhaled biomarkers, can be indicators of certain diseases if present in unusual quantities in a person's breath. Chemical detection can also be used as a warning system for potential threats from chemical, biological, and energetic (i.e., explosives) weapons. Furthermore, chemical detection can be used to alleviate the growing concern of air quality in large buildings, where chemicals can accumulate within confined spaces of the buildings.